This invention relates to an infinitely variable speed transmission of the drive chain sprocket type particularly adapted to bicycles.
Variable speed transmissions for bicycles are of course well known and are generally positioned between the bicycle pedals and the rear wheel in order to change the transmission drive ratio in accordance with the effort required to propel the bicycle. One of the most popular variable speed bicycle transmissions in present use is of the "Derailleur" type wherein the bicycle sprocket chain is "derailed" or shifted between several different size sprockets on the rear wheel in order to effect a change in drive ratio. In this type of variable or plural speed transmission, there is a brief interruption in transmission of torque during each change in drive ratio which is furthermore manually initiated.
Change speed bicycle transmissions of the infinitely variable types are also known wherein a change in drive ratio is effected through a radially expansible or contractible sprocket gear assembly mounted on or driven by the bicycle pedal assembly. Such a variable speed transmission is disclosed for example in U.S. Pat. No. 724,449 to Dumaresq. In the latter type of bicycle transmission, the pedal driven, expansible sprocket wheel has a plurality of sprocket pinions mounted on a wheel plate for radial adjustment to different positions in order to determine the effective drive wheel diameter at which the sprocket pinions engage the sprocket chain. The use of an angularly displaceable control disk having spiral grooves engaging radially displaceable elements on an expansible sprocket wheel in a bicycle transmission, is also known as disclosed in U.S. Pat. No. 598,654 to Cleland. Radially expansible sprocket wheel driving devices for variable speed bicycle transmissions wherein spring means biases the chain engaging sprocket pinions to the maximum drive ratio position, for input torque responsive variation in drive ratio, is also known as disclosed for example in U.S. Pat. No. 2,584,447 to Hayot.
It will be apparent that while the expansible sprocket types of bicycle transmissions provide an infinitely variable drive ratio avoiding the torque transmission interruptions of plural step speed transmissions of the Derailleur type, they are characterized by undesirable cyclic fluctuations in drive ratio not present in a Derailleur type of transmission. Automatically controlled bicycle transmissions of the infinitely variable speed type ordinarily respond to cyclic variations in effort applied through the pedal assembly to cause undesirable oscillations and drive ratio fluctuations. It is therefor an important object of the present invention to provide an automatically controlled bicycle transmission that avoids the drawbacks aforementioned. A further object is to provide a variable speed bicycle transmission wherein the drive ratio changes are effected without interruption in the transmission of torque between the pedals and the rear wheel propelling the bicycle.